Technical Field
Embodiments of the subject matter disclosed herein generally relate to reciprocating compressors, and more particularly, to a pressure packing for a reciprocating compressor.
Discussion of the Background
A reciprocating compressor frame typically includes a crankcase, crosshead guide, distance piece and cylinder. An oil lubricated and bearing mounted crankshaft in the crankcase is rotated by way of an input shaft connected to a prime mover such as an internal combustion engine. A connecting rod extends between the crankshaft and a cross-head slidably mounted in the crosshead guide. The crosshead guide guides the cross-head and connecting rod to convert the rotating motion of the crankshaft into a reciprocating linear motion at the cross-head. A distance piece, discussed further below, is disposed between the crosshead guide and the cylinder and a piston rod connected to the cross-head extends through the distance piece to a piston in the cylinder. A first one way valve at the cylinder body allows process gas to be drawn into the cylinder during the suction stroke and another one way valve at the cylinder body allows process gas to exit the cylinder upon reaching a predetermined pressure. In this manner, a process gas, for example, natural gas, may be compressed for use, further processing, and/or transport.
The typical distance piece includes a pressure packing extending around the piston rod to seal the cylinder and piston and rod assembly of the compressor. A piston rod wiper may also be included in the distance piece to remove lubricant deposited on the piston rod from the crankcase side.
The distance piece may be configured to provide a separation distance between the crank end side and the cylinder to prevent cross-contamination between compressor lubricant and process gas. More specifically, a compartment in the distance piece may be configured with a length sufficient to prevent any part of the reciprocating piston rod from entering both the piston rod wiper and the pressure packing. An oil slinger may also be included on the piston rod in the compartment to inhibit migration of lubricant toward the pressure packing.
For further sealing control and prevention of cross-contamination, a distance piece may be provided with an inboard compartment, discussed above, and an outboard compartment separated from the inboard compartment by a partition wall including a partition seal. Other types of controls may also be implemented, for example, the inboard and/or outboard distance piece may be configured to be purged with an inert gas vented to a sealed container. As another example, coolant and/or lubrication may be separately provided to the pressure packing in the outboard compartment.
The type of distance piece that is used, e.g., single compartment or inboard/outboard compartment, and the manner in which the distance piece and/or the pressure packing are managed, e.g., by purging, venting, etc., may be determinative of what type of process gas may be compressed with the reciprocating compressor, see for example, Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services, API Standard 618, and/or Specification for Packaged Reciprocating Compressors for Oil and Gas Production Services published by the American Petroleum Institute, ISO 13631, and incorporated herein by reference. For example, natural gas generally free of hydrogen sulfide, so-called sweet gas, may be compressed with a single compartment reciprocating compressor. However, natural gas including significant amounts of hydrogen sulfide, so-called sour gas, and other gases considered hazardous, corrosive, or otherwise toxic are oftentimes required to be compressed by a reciprocating compressor having a distance piece with two compartments. Such compressors may further require purging and venting of the pressure packing between the distance piece and the cylinder assembly.
If a reciprocating compressor is used in a location where the process gas changes from sweet gas to sour gas, it may be necessary to reconfigure the compressor with a two compartment distance piece so that further control may be applied to the process gas. This change oftentimes requires modifying or replacing other compressor components to accommodate the change, for example, a longer piston rod may be required to accommodate the second compartment of the two compartment distance piece. Oftentimes the entire footprint of the reciprocating compressor is also affected and thus, further time and expense must be invested to change components located peripherally of the compressor. Not only are these changes time consuming, expensive, and oftentimes difficult to carry out, the additional components introduced to the compressor add a greater level of mechanical complexity and thus render the compressor more prone to failures such as leaking.
What is needed then is a reciprocating compressor, and more particularly, a pressure packing, which allows the reciprocating compressor to be more readily converted to compress different types of gas, to be more easily serviced, and to be more reliable and less prone to leakage.